Chronic relapsing intestinal inflammation appears to be mediated by dysregulated innate and acquired immune responses to commensal (nonpathogenic) bacteria in genetically predisposed individuals. We previously demonstrated that interleukin - 10 deficient (IL-10-/-) mice selectively colonized (monoassociated) with non-pathogenic strains of Escherichia coli (NC101) or Enterococcus faecalis (OG1RF) develop different phenotypes of colitis with clear regional and kinetic differences, and that different E. coli strains differentially induce colitis in monoassociated IL-10-/- mice. The selective ability of the different E. coli strains to cause colitis correlates with the degree of epithelial adherence in vivo, epithelial intracellular invasion in vitro, and intracellular persistence in macrophages. We also have shown that several bacterial virulence factors shared by uropathogenic E. coli strains are increased in our colitogenic NC101 E. coli strain and several adherent/invasive E. coli (AIEC) strains isolated from Crohn's disease patients.3 Therefore, we hypothesize that E. coli- associated virulence factors that mediate bacterial mucosal adherence, invasion, and intracellular survival are increased in children with Crohn's disease with genetic polymorphisms that mediate bacterial killing versus children with ulcerative colitis and healthy individuals. We also hypothesize that there is regional specificity of these bacterial virulence factors in Crohn's ileitis versus colitis. Ultimately, the induction of Crohn's disease requires both host genetic susceptible and expression of specific bacterial genes. These hypotheses are addressed by the following Specific Aims: Specific aim 1: Characterize the frequency of mucosally - adherent E. coli, and E. coli - associated virulence factors from mucosal biopsy samples (a) in the ileum and different regions of the colon of children with Crohn's disease versus children with ulcerative colitis, and control individuals (normal controls and self-limited infectious colitis), and (b) between different regions of the intestine within children with Crohn's disease. Specific aim 2: Determine if polymorphisms of genes that regulate bacterial processing and killing (NOD2, ATG16L1, IRGM) are associated with (a) mucosal colonization in the intestine of AIEC, and (b) increased E. coli virulence gene expression in children with Crohn's disease This application will delineate host - genetic interactions with functionally altered E. coli and their associated virulence genes in children and adolescents with IBD and correlating these findings with host genotype. PUBLIC HEALTH RELEVANCE: Completion of this proposal will identify specific dominant E. coli virulence genes present at a higher frequency in pediatric Crohn's disease and regional specificity of these factors and correlate their presence with disease genotype. In addition, these studies will delineate host - genetic interactions with functionally altered E. coli and their associated virulence genes. Ultimately, these studies will help us develop a better understanding of the relationship between commensal organisms such as E. coli, the genetically susceptible individual's ability to process these organisms, and subsequent metabolic pathways involved in disease pathogenesis.